Slotted diaphragm semiconductor device

ABSTRACT

An integrated semiconductor device includes a semiconductor body with a first surface having a predetermined orientation with respect to a crystalline structure in the semiconductor body. The semiconductor body has a depression formed into the first surface of the body. A layer of thin film material covers at least a portion of the first surface and includes an electric, thermal-to-electric, or electric-to-thermal element. The diaphragm apparatus forms a slotted diaphragm substantially covering the depression. The slotted diaphragm includes one or more slots sized and oriented so that, in the fabrication of the device, an anisotropic etch placed on the slot or slots will completely undercut the diaphragm and form the depression. The electric, thermal-to-electric, or electric-to-thermal element is substantially supported by the diaphragm and, therefore, is substantially thermally and physically isolated from the semiconductor body.

BACKGROUND AND SUMMARY OF THE INVENTION

This application is a continuation-in-part of application Ser. No.656,301, filed Oct. 1, 1984, now abandoned, which, in turn, is acontinuation-in-part of application Ser. No. 431,538, filed Sept. 30,1982.

Devices of the type disclosed in application Ser. No. 512,079, now U.S.Pat. No. 4,472,239 and in application Ser. No. 431,538, now U.S. Pat.No. 4,478,077 included generic structures and flow sensors which arewell suited for many applications. These earlier designs, for example,provide high sensitivity flow sensing, particularly at low flow rates.For high velocity flows, however, the relatively delicate structures ofthe earlier disclosed designs can be destroyed by high velocity airflows. Further, for some applications it is desirable to provide asensor on a smaller area of the semiconductor device. The presentinvention solves both of these problems.

The present invention comprises a semiconductor device and a method forfabricating the semiconductor device.

The semiconductor device comprises a semiconductor body with a firstsurface having a predetermined orientation with respect to a crystallinestructure in the semiconductor body. The semiconductor body has adepression formed into the first surface of the body. A layer of thinfilm material covers at least a portion of the first surface. Diaphragmapparatus comprising the layer of thin film material and furthercomprising a static electric element forms a slotted diaphragmsubstantially covering the depression. The slotted diaphragm comprises aslot sized and oriented so that, in the fabrication of the device, ananisotropic etch placed on the slot will undercut the diaphragm and formthe depression. The static electric element is substantially supportedby the diaphragm and therefore is substantially thermally and physicallyisolated from the semiconductor body. The present invention furthercomprises a method of fabricating a slotted diaphragm semiconductordevice comprising a slotted diaphragm of thin film materialsubstantially covering a depression etched into a first surface of asemiconductor body. The method comprises the steps of providing asemiconductor body with a first surface having a predeterminedorientation with respect to a crystalline structure in the semiconductorbody. The method further comprises applying a layer of thin filmmaterial of which the diaphragm is comprised onto the first surface andexposing an area of the first surface through a slot in the layer of thethin film material The slot is sized and oriented so that an anisotropicetch placed on the exposed surface area will undercut the diaphragm andform the depression. The method also comprises applying the anisotropicetch to the exposed surface area to undercut the diaphragm and createthe depression. The anisotropic etch has one of the etch compositionsthat causes the etching action to substantially terminate at the (111)planes as is well known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3, 5 and 5A illustrate alternate preferred embodiments of flowsensors constructed in accordance with the present invention; and

FIG. 4 illustrates circuitry for operating the disclosed flow sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Structures in accordance with the present invention have manyapplications. The present invention is disclosed using an example ofalternate preferred embodiments of a flow sensor compatible with thepresent invention. The present invention, however, is not limited toflow sensors.

Structures in accordance with the present invention typically comprisestatic electric, thermal-to-electric, and/or electric-to-thermalelements, supported by a slotted diaphragm substantially covering adepression in a semiconductor body.

The present invention comprises an integrated semiconductor devicecomprising a semiconductor body 20 with a first surface 36 having apredetermined orientation with respect to a crystalline structure in thesemiconductor body. Semiconductor body 20 has a depression 30 formedinto first surface 36 of the body. The present invention furthercomprises a layer 29 of thin film material covering at least a portionof first surface 36.

The present invention further comprises diaphragm means 32 comprisinglayer 29 of thin film material and further comprising a static electric,thermal-to-electric, or electric-to-thermal element such as elements 22,24 and 26 further discussed below. Diaphragm means 32 forms a slotteddiaphragm 32 substantially covering depression 30. Slotted diaphragm 32comprises a slot 82 sized and oriented so that, in the fabrication ofthe device, an anisotropic etch placed on slot 82 will undercutdiaphragm 32 and form depression 30. The static electric,thermal-to-electric, or electric-to-thermal element is substantiallysupported by diaphragm 32 and, therefore, is substantially thermally andphysically isolated from semiconductor body 20.

In a preferred embodiment, the present invention comprises asemiconductor body 20 having a depression 30 formed into a first surface36 of body 20, semiconductor body 20 comprising (100) silicon and havinga (100) plane and a <110> direction, first surface 36 of semiconductorbody 20 being substantially parallel to the (100) plane. The preferredembodiment of the present invention further comprises a layer 29 of thinfilm material covering at least a portion of first surface 36. Thepreferred embodiment further comprises diaphragm means 32 comprisinglayer 29 of thin film material and further comprising a static electric,thermal-to-electric, or electric-to-thermal element such as 22, 24 or 26as further discussed below. Diaphragm means 32 comprises a slotteddiaphragm 32 substantially covering depression 30, the slotted diaphragmcomprising slot 82 oriented at an angle 112 of substantially 45 degreesto the <110> direction and extending across depression 30 at theapproximate center of the depression. The static electric,thermal-to-electric, or electric-to-thermal element is substantiallysupported by diaphragm 32 and, therefore is substantially thermally andphysically isolated from semiconductor body 20.

As will be further discussed below, the present invention is adaptableto being configured as a flow sensor. In such configurations, a thinfilm heater 26 is supported over depression 30 by diaphragm 32. In thepreferred embodiment, approximately half of heater 26 is located on eachside of slot 82. The preferred embodiment of the present flow sensorfurther comprises a pair of thin film heat sensors 22 and 24 supportedby diaphragm 32. In the preferred embodiment, the thin film heat sensors22 and 24 are disposed on opposite sides of heater 26.

The present invention further contemplates a method or process offabricating a device of the class described having a slotted diaphragm32 of thin film material 29 substantially covering a depression 30etched into a first surface 36 of a semiconductor body 20. Contemplatedsteps include providing a semiconductor body 20 with a first surface 36having a predetermined orientation with respect to a crystallinestructure in the semiconductor body, applying a layer 29 of thin filmmaterial, comprising diaphragm 32, onto first surface 36, exposing firstsurface 36 through a slot or slots as at 82 in layer 29 of the thin filmmaterial and applying the anisotropic etch to the exposed surface areato undercut diaphragm 32 and create depression 30. Slotting is sized andoriented so that an anisotropic etch placed on the exposed surface areawill undercut diaphragm 32 and form depression 30.

A preferred method of practicing the present invention comprisesproviding a semiconductor body 20 contemplates (100) silicon and havinga (100) plane and a <110> direction, first surface 36 of thesemiconductor being substantially parallel to the (100) plane. A layerof thin film material of diaphragm 32 is added to first surface 36. Aslot 82 is fabricated through the layer of thin film material orientedat substantially 45 degrees to the <110> direction. The slot defines alength which determines the maximum width of depression 30 as measuredalong the slot oriented at substantially 45 degrees to the <110>direction. An anisotropic etch is applied to the exposed surface area toundercut diaphragm 32 and create depression 30.

In a further preferred embodiment of the present invention, depression30 is bounded at first surface 36 by a substantially squareconfiguration comprising four substantially perpendicular boundary edges111 and 113, each of the four substantially perpendicular boundary edgesbeing substantially in line with or substantially perpendicular to the<110> direction.

In this embodiment, slotted diaphragm 32 comprises slot means comprisingfirst and second slots 82A and 82B located on a line 83 oriented at anangle 112 of substantially 45 degrees to the <110> direction. Each offirst and second slots 82A and 82B comprise a first end 200A and 200Brespectively, first and second slots 200A and 200B being located at amaximum width of depression 30 as measured along line 83. Each of thefirst and second slots 82A and 82B have a second end 202A and 202Brespectively, ends 202A and 202B being located so that each of the firstand second slots 82A and 82B extend only a portion of the distanceacross the maximum width of depression 30 as measured along line 83.

The further preferred embodiment further comprises third, fourth, fifthand sixth slots 82C, 82D, 82E and 82F oriented substantially in linewith or substantially perpendicular to the 110 direction, each of thethird, fourth, fifth and sixth slots being similarily situatedsubstantially central to one of the four boundary edges 111 and 113.Each of the third, fourth, fifth and sixth slots 82C, 82D, 82E and 82Fis of a length sufficient to permit complete cooperative undercutting ofdiaphragm 32 when an isotropic etch is placed on the areas exposed byeach of the six slots as is further explained below.

When configured as a flow sensor, the further preferred embodimentcomprises a thin film heater 26 supported over depression 30 bydiaphragm 32. Approximately half of heater 26 is located on each side ofline 83. In that embodiment, a pair of thin film heat sensors 22 and 24are supported by diaphragm 32, thin film heat sensors 22 and 24 beingdisposed on opposite sides of heater 26.

The method of fabricating the further preferred embodiment comprisesexposing first and second areas of first surface 36 through first andsecond slots 82A and 82B in layer 29 of the thin film material. Firstand second slots 82A and 82B are located on a line 83 oriented atsubstantially 45 degrees to the <110> direction. Each of the first andsecond slots 82A and 82B comprise a first end 200A and 200B respectivelylocated at a maximum width of depression 30 as measured along line 83.Each of the first and second slots 82A and 82B have a second end 202Aand 202B respectively located so that each of the first and second slotsextends only a portion of the distance across the maximum width of thedepression as measured along line 83.

Third, fourth, fifth and sixth areas of first surface 36 are exposedthrough third, fourth, fifth and sixth slots 82C, 82D, 82E and 82F inthin film layer 29. The third, fourth, fifth and sixth slots 82C, 82D,82E and 82F are oriented substantially in line or substantiallyperpendicular to the 110 direction, there being one of the third,fourth, fifth and sixth slots 82C, 82D, 82E and 82F located at thesubstantial center of each of the four boundary edges 111 and 113. Eachof the third, fourth, fifth and sixth slots have a length sufficient topermit undercutting of diaphragm 32 when an anisotropic etch is placedon each of the six slots. The anisotropic etch is applied to the exposedsurface areas to undercut diaphragm 32 and create depression 30.

In a third preferred embodiment of the present invention, as in theabove-described embodiments, depression 30 is bounded at first surface36 by a configuration of pairs of substantially perpendicular boundaryedges 111 and 113, each of the four boundary edges is situatedsubstantially in line with or substantially perpendicular to the <110>direction.

In this embodiment, as depicted in FIG. 5a, slotted diaphragm 32includes slot means having a plurality of spaced, axially aligned slotsor segments as illustrated by 82G, 82H, 82I and 82J located on line 83oriented at angle 112 which is substantially 45 degrees to the <110>direction. Each of the outer slots 82G and 82J have a first or outer end300G and 300J respectively. Points 300G and 300J define the maximumwidth or extremes of depression 30 as measured along line 83. Each ofthe slots 82G and 82J have a second end 302G and 302J respectively. Ends302G and 302J are located so that each of the slots 82G and 82J extendonly a portion of the distance across the maximum width of depression 30as measured along line 83.

The additional spaced slots or segments 82H and 82I, intermediate andaligned with slots 82G and 82J, have respective ends 300H, 302H and 300Iand 302I as shown. If each of the slots be assigned an arbitrary width Wand the interslot distance separating or axial spacing of the slots 82Gthrough 82J be defined as D, the only size limitation is that W>D. Asillustrated in FIGS. 5 and 5A, if this requirement be met, slots 82Gthrough 82J present a composite exposure of surface 36 sufficient topermit complete undercutting of diaphragm 32 when an anisotropic etch isplaced on each of the slots or segments.

Thus, in the embodiment of FIG. 5, the etching proceeds beneath thediaphragm first between the slot ends as illustrated in FIG. 5a, and thenecessary requirement of the dimensions of the space between slot endsrelative to slot widths such that W>D became more apparent when theetching process is addressed in further detail. When this requirement ismet, the etching action proceeds from the end of slot 82I toward thelimit of the dashed lines 114, which limit overlaps the correspondingdashed line limit 115 of the etch proceeding from the end of slot 82J.The composite overlapping patterns of this first etching actionincluding slots 82G and 82H, creates a continuous narrow cavity a longcenterline 83 within the final etch pit boundaries 111 and 113. The etchcan then proceed laterally from this continuous narrow cavity to theetch-stop limit boundaries 111 and 113 which boundaries lie beyond thedashed line local pit limits of individual slots 82G, 82H, 82I and 82J.

The third preferred embodiment illustrates four slots or slot segments.

Of course it will readily be appreciated that the number and size of theslots used may be varied according to the particular applicationinvolved and there is nothing sacred about the number illustrated.

Body 20 is preferably a semiconductor body and preferably silicon,chosen because of its adaptability to precision etching techniques andease of electronic chip producibility. The preferred embodiment of aflow sensor in accordance with the present invention preferably includestwo identical temperature sensing resistor grids 22 and 24 acting asthin film heat sensors and further includes a centrally located heaterresistor grid 26 acting as a thin film heater. Sensors 22 and 24 andheater 26 are preferably fabricated of nickel-iron, herein sometimesreferred to as permalloy, having a preferred composition of 80 percentnickel and 20 percent iron. The sensor and heater grids are typicallyencapsulated in a thin film of dielectric, typically comprising layers28 and 29 and preferably silicon nitride to form thin film diaphragms32. The preferred embodiment of devices fabricated in accordance withthe present invention further comprise an accurately defined air space30 between diaphragm 32 and semiconductor body 20. Air space 30effectively results in an area space on each side of diaphragm 32.Effectively placing an air space on each side of diaphragm 32 isachieved by fabricating the structure on silicon surface 36, and bysubsequently etching an accurately defined air space 30 into siliconbody 20 beneath diaphragm 32.

In the embodiment illustrated in FIG. 1, slot 82 cut through nitridelayer 29 to expose an area of first surface 36 can be quite narrow, 5microns for example. The anisotropic etch removes the silicon in theform of a square depression 30 bounded by substantially perpendicularboundary edges 111 and 113, boundary edges 111 illustrated beingsubstantially in line with the <110> direction and boundary edges 113 asillustrated being substantially perpendicular to the <110> direction. Ofcourse, a wider slot will provide more rapid diffusive removal of etchproduct and thus reduce the time required to complete depression 30.

In the embodiment illustrated in FIG. 1A, the longer slot 82 illustratedin FIG. 1 is divided into two shorter slots 82A and 82B with a broadsection of silicon nitride supporting film (layers 28 and 29) connectingthe right and left sides of diaphragm 32. This connection furtherstrengthens the silicon nitride supporting film and further preventspenetration of airflow under the more vulnerable central part ofdiaphragm 32. Accordingly, the embodiment of FIG. 1A is stronger forhigh velocity flow applications than the embodiment of FIG. 1.

However, slots 82A and 82B by themselves do not permit the anisotropicetch formation of the entire desired diaphragm 32 because thecorresponding etch pits that would be created from slots 82A and 82B arelimited to the vicinity of these slots as shown by dashed lines 204A and204B respectively in FIG. 1B. Thus, it is necessary to form slots 82C,82D, 82E and 82F approximately centrally located on boarder edges 111and 113 and having a sufficient length so that the depressions formedthrough slots 82C, 82D, 82E and 82F slightly overlap the localdepressions formed through slots 82A and 82B. After the depressionsadjacent to slots 82A and 82B are formed (these local depressions beingdefined by dashed lines 204A and 204B respectively), a second stage ofetching begins, and the depression bounded previously by dashed line204A is enlarged to a larger depression bounded by dashed line 206A;similarly, the depression previously bounded by dashed line 204B isenlarged to a larger depression now bounded by dashed line 206B andoverlapping the depression bounded by line 206A. The final depressiondimensions are formed in a third and last stage of etching where regions208 are etched out, thus resulting in a square depression having thesame dimensions as in FIG. 1.

Slots 82C, 82D, 82E and 82F can be even narrower than slots 82A and 82B,3 microns for example, because the diffusive access of the anisotropicetch to the space beneath the diaphragm can be adequately provided byslots 82A and 82B, and the additional access provided by slots 82C, 82D,82E and 82F only speed up the etching process.

The operation of the present sensor in sensing air flow can be describedwith reference to FIG. 1. Heater resistor grid 26 operates at apreferred constant average temperature difference of 100-200 degreescentigrade elevated above the temperature of silicon chip 20 whichtemperature is not appreciably different from the ambient air streamtemperature.

In the preferred embodiment illustrated, sensor grids 22 and 24 areprecisely symmetrically located with respect to heater grid 26 so thatat zero airflow they have identical temperatures and have no differencesbetween their resistances. Consequently, a small probe current, 0.1-1.0milli-amperes preferred, through both sensor resistances 22 and 24 willdevelop no voltage difference at zero airflow velocity.

With airflow present, upstream sensor 22 will be cooled by thetransportation of heat away from sensor 22 toward heater resistor grid26, whereas downstream sensor 24 will be heated by a transportation ofheat toward the sensor from heat resistor grid 26. Consequently, aresistance difference between sensor resistances 22 and 24 will bepresent with a corresponding difference in voltage drop which is ameasure of the air flow. Typical unamplified voltage differences can beas high as 0.1 volt at a 1500 feet/minute flow velocity.

In the preferred operation of the present sensor, sensors 22 and 24 areoperated with constant current such that temperature field changes canbe sensed under flow conditions as previously described. Other operatingarrangements are also possible.

Because of the exceedingly small thermal mass of the heater and sensorelement structure and the thermal insulation provided by the thinsilicon nitride connecting means to the supporting silicon body, andbecause of the surrounding air space, response time of the presentsensor is very short, with response time constants of 0.005 secondshaving been measured. Consequently, sensor elements 22 and 24 canrespond very rapidly to air flow changes.

In the preferred embodiment of the present sensor, ambient temperatureis monitored by a reference resistor 38 which is heat sunk ontosemiconductor body 20. Resistor 38 may be a permalloy grid formedsubstantially like grids 22, 24 and 26 and is typically encapsulated indielectric layers 28 and 29 and mounted on surface 36.

The typical 0.8 micron total thickness of dielectric layers 28 and 29 isvery thin and, accordingly, permits relatively good heat conduction andtransfer perpendicular to the layers to and from resistive grids 22, 24,26 and 38. Thus, reference resistor 38, being attached by theencapsulating dielectric directly to surface 36 of semiconductor body20, readily monitors the temperature of the semiconductor body, whichstays within 0.5 degrees centigrade of ambient temperature even withresistor grid 26 elevated to 200 degrees centigrade above ambient.Accordingly, heat sunk reference resistor 38 may be used to monitorambient air flow temperature by monitoring a temperature that is veryclose to that of semiconductor body 20, which in turn is very close toambient temperature.

As previously indicated in the preferred operation of the presentsensor, heater 26 is operated at a constant temperature above ambienttemperature, sensors 22 and 24 being operated at constant current, andthe changing temperatures of sensors 22 and 24 are sensed as changes inresistance. Circuits for accomplishing these functions are illustratedin FIG. 4. The smaller circuit controls the temperature of heater 26while the larger circuit provides an output voltage that is proportionalto the resistance difference between heat sensing resistors 22 and 24.

The heater control circuit illustrated in FIG. 4 uses a wheatstonebridge 46 to maintain heater 26 at a constant temperature rise aboveambient as sensed by heat sunk reference resistor 38. Wheatstone bridge46 is shown comprising heater resistor 26 and a resistor 40 in its firstleg and a resistor 42, heat sunk resistor 38 and a resistor 44 in itssecond leg. An error integrator comprising amplifier 50 keeps bridge 46balanced by varying the potential across it and thus the powerdissipated in heater 26.

The circuity which monitors the resistance difference between downstreamsensor 24 and upstream sensor 22 includes a constant current source 52comprising an amplifier 72 and a differential amplifier 54 comprisingamplifier 68 and 70. The constant current source drives a wheatstonebridge comprising two high impedance resistors 56 and 58 in one leg andthe two sensing resistors 22 and 24 with a nulling potentiometer 60 inthe other leg. The gain of differential amplifier 54 is adjusted bypotentiometer 62. Output 64 provides a voltage that is proportional tothe resistance difference between the two sensing resistors 22 and 24.

Amplifiers 50, 66 and 72 may each comprise one-fourth of an LM324.Amplifiers 68 and 70 may each comprise one-half of an OP-10.

Upstream sensor resistor 22 preferably has an inner edge 76 in closeproximity (5 to 10 microns, for example) to the near edge 78 of heaterresistor grid 26 At such a separation from near edge 78 of heaterresistor grid 26, the zero flow air temperature near heater resistoredge 78 is close to that of edge 78. In a typical embodiment, wheresensors 22 and 24 have a width of approximately 100 microns, outer edge80 of sensor resistor grid 22 is located approximately 100 microns fromnear edge 78 of heater resistor grid 26. At the 100 micron separation,the zero airflow temperature is closer to that of the ambient air streamand to that of silicon chip 20 than it is to the temperature of heaterresistor 26.

Therefore, outer edge 80 of sensor resistor grid 22 is easily cooled tonear the limiting temperature of silicon chip 20 by low velocityairflow, whereas the inner regions of sensor resistor grid 22 (near edge76) are more tightly coupled thermally to heater resistor 26 and respondmore readily to the higher airflow velocity before the limitingtemperature of the ambient airstream is approached. Accordingly, thecomposite effect of the temperature change from each resistor grid line(lines spaced over the approximately 5-100 micron distance from heateredge 76) for an increment of airflow is to keep the correspondingincrement on the upstream resistor temperature response curve morenearly constant over a broad airflow range.

As shown in FIG. 1, area 82 (and areas 82A-82F) are cut in the siliconnitride to facilitate etching as further described below. Overallgeometry, including that of leads 92, is preferably made symmetricallyto insure symmetrical heat conduction properties. Leads 92 connect topad areas 90 for electrically connecting sensor elements 22, 24, 26, and38 with circuitry 13 as previously discussed.

Elements 22 and 24 have a preferred resistance in one example of 1200ohms and element 26 has a preferred resistance in that example of 520ohms. In this embodiment, sensors 22 and 24 have a width ofapproximately 100 microns and a length of approximately 175 microns. Aspreviously indicated, in this example the proximal edges of sensors 22and 24 are in close proximity (e.g., 5-10 microns) away from heater 26.That is, edge 76 of sensor 22 is 5-10 microns away from edge 78 ofheater 26, and edge 84 of sensor 24 is 5-10 microns away from edge 86 ofheater 26.

As with other dimensions listed in the present application, the abovedimensions are preferred dimensions which have been used in actualdevices and are not deemed to be limiting, since these parameters couldbe substantially varied depending upon application.

The preferred process of fabricating the present sensor comprisesproviding a (100) silicon wafer 20 having a surface 36 which receives alayer 29 of silicon nitride. Layer 29 is typically 4000 angstroms thickand is typically deposited by standard sputtering techniques in a lowpressure gas discharge. Next, a uniform layer of permalloy, typically80% nickel and 20% iron and 800 angstroms thick, is deposited on thesilicon nitride by sputtering.

Using a suitable photo mask, a photoresist and a suitable etchant,permalloy elements such as 22, 24, 26 and 38 are delineated. A secondlayer 28 of silicon nitride, typically 4000 angstroms thick, is thensputter-deposited to provide complete coverage of the permalloyconfiguration and thus protect the resistive element from oxidation.Openings such as 82 and 82A-82F are then etched through the nitride tothe (100) silicon surface in order to delineate slotted diaphragm 32.The relative sizes of openings such as 82 and 82A-82F are largely amatter of design choice.

Anisotropic etchant that does not appreciably attack the silicon nitrideis used to etch out the silicon in a controlled manner from beneathdiaphragm 32 (KOH plus Isopropyl alcohol is a suitable etchant). Thesides of the etched depression such as 30 are bounded by (111) and othercrystal surfaces that are resistive to the etchant. The depressionbottom, a (100) surface which is much less resistant to the etchant, islocated at a specified distance (e.g., 125 microns) from the members,typically by adjusting the duration of the etch. A doped silicon etchstop (e.g., a boron-doped layer) may also be used to control the depthof the depression, although such stops are not typically necessary whenfabricating the present sensor. By adjusting the duration of the etch,the depth of depressions such as 30 can be controlled to a precision ofabout three microns or to about two percent. This precision results in aprecise reproducibility of the thermal conductance of the air spacesurrounding diaphragm 32 and a correspondingly precise reproducibilityof air flow response.

FIG. 3 shows a region 116 for integration of circuitry, for example,portions of the circuitry illustrated in FIG. 4.

For the embodiments shown, diaphragm 32 is typically 0.8-1.2 micronsthick. Typical permalloy elements such as elements 22, 24, 26 and 38have a thickness of approximately 800 angstroms (typically in the rangeof approximately 800 angstroms to approximately 1600 angstroms) with apreferred composition of 80% nickel and 20% iron and a resistance valuewithin the range of approximately 200 ohms to approximately 2000 ohms atroom temperature, e.g., at approximately 20-25 degrees centigrade (atpermalloy element temperatures up to approximately 400 degreescentigrade resistance values increase by a factor of up to approximately3). Line widths within permalloy grids may be approximately 5 micronswith a 5 micron spacing. Depressions such as 30 typically have a 0.005inch (125 micron) depth spacing between members such as 32 and 34 andthe semiconductor body such as 20, but the spacing can easily vary inthe range of approximately 0.001 inch to approximately 0.010 inch. Atypical thickness of the semiconductor body or substrate such as 20 is0.008 inch. (As previously indicated, dimensions provided areillustrative only and are not to be taken as limitations.)

Typical operating temperatures of heater elements such as 26 are in therange of approximately 100-200 degrees centigrade with approximately 160degrees centigrade above ambient being the preferred operatingtemperature. Using the preferred permalloy element, this can beaccomplished with only a few milliwatts of input power.

A heater resistance element having a 200-1000 ohm preferred resistanceat 25 degrees centigrade provides the desired power dissipation toachieve the preferred operating temperature at a convenient voltage of afew volts and a convenient current of, for example, 2 to 5 milliamperes.

The present invention is to be limited only in accordance with the scopeof the appended claims since persons skilled in the art may devise otherembodiments still within the limits of the claims.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:
 1. An integrated semiconductordevice, comprising:a semiconductor body with a first surface having apredetermined orientation with respect to a crystalline structure in thesemiconductor body, the semiconductor body having a depression formedinto the first surface of the body; a layer of thin film dielectricmaterial covering at least a portion of the first surface; and a slotteddiaphragm comprising the layer of thin film material and furthercomprising an electric element, the slotted diaphragm substantiallycovering the depression, the slotted diaphragm further comprising asingle slot extending across the diaphragm from one extremity to theother, the slot having first and second ends intersecting the firstsurface of the semiconductor body, the slot being substantially centeredon the diaphragm and being oriented so that, in the fabrication of thedevice, an anisotropic etch placed on the slot will undercut thediaphragm and form the depression, the electric element beingsubstantially supported by the diaphragm and, therefore, substantiallythermally and physically isolated from the semiconductor body.
 2. Theapparatus of claim 1 wherein the static electric element comprises athermal-to-electric transducing element.
 3. The apparatus of claim 1wherein the electric element comprises an electric-to-thermaltransducing element.
 4. The apparatus of claim 1 wherein the electricelement comprises a permalloy element.
 5. The apparatus of claim 2wherein the electric element is a permalloy element.
 6. The apparatus ofclaim 5 wherein the electric element is a permalloy element.
 7. Theapparatus of claim 1 wherein the dielectric material comprises siliconnitride.
 8. The apparatus of claim 2 wherein the dielectric materialcomprises silicon nitride.
 9. The apparatus of claim 3 wherein thedielectric material comprises silicon nitride.
 10. The apparatus ofclaim 4 wherein the dielectric material comprises silicon nitride. 11.An integrated semiconductor device, comprising:a semiconductor bodyhaving a depression formed into a first surface of the body, thesemiconductor body comprising (100) silicon and having a (100) plane anda <110> direction, the first surface of the semiconductor body beingsubstantially parallel to the (100) plane; a layer of thin filmdielectric material covering at least a portion of the first surface;and a slotted diaphragm comprising the layer of thin film material andfurther comprising an electric element and forming a slotted diaphragmsubstantially covering the depression, a single slot extending acrossthe diaphragm from one extremity to the other, the slot having first andsecond ends intersecting the first surface of the semiconductor body,the slot being oriented at substantially 45 degrees to the <110>direction and extending across the depression at the approximate centerof the depression, the static electric element being substantiallysupported by the diaphragm and, therefore, substantially thermally andphysically isolated from the semiconductor body.
 12. The apparatus ofclaim 11 wherein the static electric element comprises athermal-to-electric transducing element.
 13. The apparatus of claim 11wherein the electric element is an electric-to-thermal transducingelement.
 14. The apparatus of claim 11 wherein the electric elementcomprises a permalloy element.
 15. The apparatus of claim 12 wherein theelectric element comprises a permalloy element.
 16. The apparatus ofclaim 13 wherein the electric element comprises a permalloy element. 17.The apparatus of claim 11 wherein the dielectric material comprisessilicon nitride.
 18. The apparatus of claim 12 wherein the electricelement comprises a permalloy element.
 19. A flow sensor comprising:asemiconductor body having a depression formed into a first surface ofthe body, the semiconductor body comprising (100) silicon and having a(100) plane and a <110> direction, the first surface of thesemiconductor body being substantially parallel to the (100) plane; alayer of thin film material covering at least a portion of the firstsurface and forming a slotted diaphragm substantially covering thedepression, the slotted diaphragm comprising slot means oriented atsubstantially 45 degrees to the <110> direction and extending across thedepression at the approximate center of the depression; a thin filmheater supported over the depression by the diaphragm, approximatelyhalf of the heater being located on each side of the slot; and a pair ofthin film heat sensors supported by the diaphragm, the thin film sensorsbeing disposed on opposite sides of the heater.
 20. The apparatus ofclaim 19 wherein the heater is operated at a temperature elevated aboveambient, thus creating a no-flow temperature gradient in the air aboveand adjacent to the heater, the temperature within the no-flow gradientmaking a transition between the elevated temperature and substantiallyambient temperature, the sensors being located sufficiently close to theheater to be located substantially within the no-flow temperaturegradient.
 21. The apparatus of claim 19 wherein the thin film heater andsensors each comprise a permalloy element.
 22. The apparatus of claim 19wherein the layer of thin film material comprises a dielectric material.23. The apparatus of claim 22 wherein the dielectric material comprisessilicon nitride.
 24. The apparatus of claim 19 wherein the sensors arelocated from the heater at a preferred distance which, when contrastedto an alternate distance, provides a substantially greater change in theheat being delivered to the sensors for a given change in flow rate. 25.The apparatus of claim 24 wherein the heater is operated at atemperature elevated above ambient, thus creating a no-flow temperaturegradient in the air above and adjacent to the heater, the temperaturewithin the no-flow gradient making a transition between the elevatedtemperature and substantially ambient temperature, the sensors beinglocated sufficiently close to the heater to be located substantiallywithin the no-flow temperature gradient.
 26. The apparatus of claim 24wherein the thin film heater and sensors each comprise a permalloyelement.
 27. The apparatus of claim 24 wherein the layer of thin filmmaterial comprises a dielectric material.
 28. The apparatus of claim 22wherein the dielectric material comprises silicon nitride.
 29. Theapparatus of claim 28 wherein the proximal edges of the sensors arelocated from the near edges of the heater at a distance within the rangeof approximately 5 microns to approximately 25 microns.
 30. Theapparatus of claim 29 wherein the heater is operated at a temperatureelevated above ambient, thus creating a no-flow temperature gradient inthe air above and adjacent to the heater, the temperature within theno-flow gradient making a transition between the elevated temperatureand substantially ambient temperature, the sensors being locatedsufficiently close to the heater to be located substantially within theno-flow temperature gradient.
 31. The apparatus of claim 29 wherein thethin film heater and sensors each comprise a permalloy element.
 32. Theapparatus of claim 29 wherein the layer of thin film material comprisesa dielectric material.
 33. The apparatus of claim 32 wherein thedielectric material comprises silicon nitride.
 34. The apparatus ofclaim 19 wherein the heater and each sensor comprise a resistive elementhaving a pattern of resistive material formed in lines having a linewidth, the lines being separated by substantially a line width, thesensors being separated from the heater by a distance in the range ofapproximately one line width to approximately five line widths.
 35. Theapparatus of claim 34 wherein the heater is operated at a temperatureelevated above ambient, thus creating a no-flow temperature gradient inthe air above and adjacent to the heater, the temperature within theno-flow gradient making a transition between the elevated temperatureand substantially ambient temperature, the sensors being locatedsufficiently close to the heater to be located substantially within theno-flow temperature gradient.
 36. The apparatus of claim 34 wherein thethin film heater and sensors each comprise a permalloy element.
 37. Theapparatus of claim 34 wherein the layer of thin film material comprisesa dielectric material.
 38. The apparatus of claim 37 wherein thedielectric material comprises silicon nitride.
 39. An integratedsemiconductor device, comprising:a semiconductor body with a firstsurface having a predetermined orientation with respect to a crystallinestructure in the semiconductor body, the semiconductor body having adepression formed into the first surface of the body; a layer of thinfilm dielectric material covering at least a portion of the firstsurface; a slotted diaphragm comprising the layer of thin film materialand further comprising an electric element, the slotted diaphragmsubstantially covering the depression, wherein the slotted diaphragmfurther comprises a slot means including a plurality of spaced axiallyaligned slots extending across the diaphragm from one extremity to theother, each said slot exposing a defined area of the first surface ofthe semiconductor body, the axial separation between said slots beingless than the slot width, the slot means being substantially definingthe center of the diaphragm and being oriented so that, in thefabrication of the device, an anisotropic etch placed in each slot willundercut the diaphragm and form the depression, the static electricelement being substantially supported by the diaphragm and, therefore,substantially thermally and physically isolated from the semiconductorbody.
 40. The apparatus of claim 39 wherein the static electric elementcomprises a thermal-to-electric transducing element.
 41. The apparatusof claim 39 wherein the electric element comprises anelectric-to-thermal transducing element.
 42. The apparatus of claim 40wherein the electric element comprises a permalloy element.
 43. Theapparatus of claim 41 wherein the electric element comprises a permalloyelement.
 44. The apparatus of claim 39 wherein the dielectric materialcomprises silicon nitride.
 45. The apparatus of claim 40 wherein thedielectric material comprises silicon nitride.
 46. The apparatus ofclaim 41 wherein the dielectric material comprises silicon nitride. 47.The apparatus of claim 42 wherein the dielectric material comprisessilicon nitride.
 48. An integrated semiconductor device, comprising:asemiconductor body having a depression formed into a first surface ofthe body, the semiconductor body comprising (100) silicon and having a(100) plane and a <110> direction, the first surface of thesemiconductor body being substantially parallel to the (100) plane; alayer of thin film dielectric material covering at least a portion ofthe first surface; and a slotted diaphragm comprising the layer of thinfilm material and further comprising an electric element, the slotteddiaphragm substantially covering the depression, wherein the slotteddiaphragm further comprises a slot means including a plurality of spacedaxially aligned slots extending across the diaphragm from one extremityto the other, each said slot exposing a defined area of first surface ofthe semiconductor body, The axial separation between said slots beingless than the slot width, the slot means being substantially centered onthe diaphragm, and being oriented so that, in the fabrication of thedevice, an anisotropic etch placed in each slot will undercut thediaphragm and form the depression, the static electric element beingsubstantially supported by the diaphragm and, therefore, substantiallythermally and physically isolated from the semiconductor body.
 49. Theapparatus of claim 40 wherein the static electric element comprises athermal-to-electric transducing element.
 50. The apparatus of claim 48wherein the electric element comprises an electric-to-thermaltransducing element.
 51. The apparatus of claim 49 wherein the electricelement comprises a permalloy element.
 52. The apparatus of claim 59wherein the electric element comprises a permalloy element.
 53. Theapparatus of claim 48 wherein the dielectric material comprises siliconnitride.
 54. The apparatus of claim 49 wherein the electric materialcomprises silicon nitride.
 55. The apparatus of claim 50 wherein thedielectric material comprises silicon nitride.
 56. The apparatus ofclaim 51 wherein the dielectric material comprises silicon nitride. 57.The apparatus of claim 19 wherein said slot means comprises a pluralityof spaced axially aligned slots extending across the diaphram, the axialseparation between said slots being less than the slot width.